US2366570A - Treatment of hydrocarbons - Google Patents

Description

' Jan. 211945 M. soUDERs, JR., ET AL 2,366,570

TREATMENT OF HYDROCARBONS Filed May 26, 1942 Patented Jan.` 2, 1945 n UNITED STATES t PATENT OFFICE TREATMENT OFRHYDROCARBONS Mott Souders, J r., Berkeley, and Russell N. Shiras,` y

Oakland, Calif., assignors to Shell Development i Company, San Francisc of Delaware o, Calif., a corporation Application May 26, 1942, serial No. 444,607 scleims. romeo- 680) y y This invention relates to a process forthe preparation of unsaturated hydrocarbons from petroleum distillates and, more particularly, of

` i aromatics such as toluene and diolefines, such as butadiene, isoprene, and other homologous diolenes, andis a continuation-impart of the invention described in our co-pending applica- `tion Serial No. 406,274, iiledAugust 11,` 1941.

` It has heretofore been proposed to separate aromatics, e. Vg. toluene, from natural or cracked petroleum distillates by concentrating the toluene through distillation to obtain a `concentrate `containing upwards of 5% toluene, and by exp tracting the resulting concentrate within `the l vapor phase with a suitable selective solvent to obtain pure or substantally pure toluene. It,`

has, further, been proposed to produce butadiene and similar dioleiines by pyrolysis of various hydrocarbonseither with orwithout catalysts, followed by the concentration and `separation of the dioleflnes from the conversion products byA means ofsolvents or by chemical treatment.

According to the present inventionwit was found that the yield ofaromatiosjcan be considerably improved, and that an excellent conversion to dioleflnes can `be effected by subjecting certain hydrocarbon fractions which are associated with aromatics and are in general containedin aromatic concentrates and from which the aromatics may be removed by treatment with sol-` vents, to pyrolysis under conditions favoring the formation of unsaturated hydrocarbonshaving l conjugated double bonds, and then separating l these"val'uable hydrocarbons. During this lastnamed separationit is preferred to' concentrate the aromatics contained in the crackedproducts narrow fractions are preferably produced continuous fractionation and if so `produced will, in general, upon being subjected to analytical distillation, show at least 95% boiling within the l following ranges:

Maximum vPreferred Concentrate containing range range F. F. Benzene 156-1185 164478 Toluene l95-245 206-231 Xylenes and ethyl benzene T... 260-300 267-290 Analytical distillation as herein defined is e `laboratory batch distillation operated over 30 equilibrium plates and at a reflux ratio of at i least 20:1.

" Forthe purpose of our invention the composition of the concentrates may be said to `consist of 3 `component parts: (y1) `an aromatic or a group of metameric aromatic hydrocarbons, (2) nonaromatic desirable hydrocarbons which form upon cracking large amounts of dienes, and (3) non-aromatic, less desirable hydrocarbons which in narrow boiling fractions and recycle the resulting concentrates to the solvent separation steps.

y A hydrocarbon fraction lto be` suitable for the purpose of this `invention is `onefin which has been concentrated` the major amount and preferably substantiallythe entire amount of a sin- `gle aromatichydrocarbon or `a single `group of metameric aromatic hydrocarbons, e.` g., benzene, ortoluene,` or` Xylenes `and ethyl benzene, etc., which amount was originally containedin the hydrocarbon `distillate under treatment. This fraction or concentrate should have a boiling range asnarrow as possible `consistent with the requirement of containing the major portion of the aromatic, and it should be substantially free of components boiling above or below the boiling range over which the aromatic boils when the fraction is subjected to a `close `fractional` distillationa,

,In producing these suitable concentrate fractions, highly` eilicient fractional reux ratio of 24:1 should ybe employed. Such distillation i equivalent at least to 20 theoretical plates ata simple fractional distillation is capable of` separating the desirable non-aromatic' hydrocarbons which boil higher from the less desirable nonaromatics which boil lower.

The above-defined concentrates, particularly if containing only minor amounts of aromatics, may when separated from a straight run-distillate give higher yields of dienes upon Vapor phase` cracking than higher' or lower boiling fractions or `than the petroleum` distillate from which the concentrateaare separated.` l The mixture of non-aromatic hydrocarbons including both the desirable ones and the less desirable ones, which is obtained by separating the aromatic hydrocarbons from the `remainder of the concentrate, gives higher yields of dienes than the concentrate itself. 'Ihe particularly desirable none-aromatic hydrocarbon obtained from this mixture by fractional distillation produces by `cracking still higher yieldsof Idienes.

It will be apparent that narrower fractions than the above-described may be used with advantage and that inclusion of small amounts of higher or lower boiling hydrocarbons will give inferior results, the extent of depreciation depending upon the amount of these hydrocarbons included. Such variations may be produced, for example, by less emcient fractionation of the petroleum distillate when producing the narrow boiling fractions.

Fractions boiling in the above range, particularly the preferred range, allow also the separation of pure aromatics practically free of other hydrocarbons and boiling within 1 F.

The nature of the invention will be better understood fromA the following detailed description, taken together with the drawing forming a part of this specication which illustrates certain preferred embodiments thereof, in which:

Figure I is a flow diagram illustrating a particularly preferred form of the improved process; and

Figure II is a ow diagram illustrating the general steps of the process.

For simplicity the drawing does not showpumps, heat exchangers, valves, lay-passes, vents, reboilers, condensers, and other auxiliaries, the proper placement of which will be at once evident to those skilled in the art.

Referring to Figure I, which illustrates the process of this invention as applied to the toluene concentrate, I and 2 are fractional distillation columns provided with conventional reboilers, condensers, etc. and equipped with bubble trays or other contact means, not shown. The hydrocarbon feed mixture containing toluene is introduced through line 3 from a source not shown. It may be of any provenience, either cracked or straight-run, although straight-run gasoline which contains 'appreciable quantities of toluene are preferred. Toluene-rich naphthas produced in the process, as hereinafter de` scribed, may be added thereto through line 6L As large a portion of the hydrocarbon as is practical for the retention of most of the toluene' in the bottom product is taken off overhead atl For example, it was found convenient to 4. remove overhead material boiling below 206 F. I'he distillation residue is taken off at 9 and fed into the column 2, wherein as small a proportionv of hydrocarbons as is practical for the recovery of most of the toluene in the overhead is taken off as a distillate at I0. For example, the distillate may include materials boiling below 231 F. The bottom product from column 2 is withdrawn at II.

in the feed. The columns I and 2 may, however.

be operated to other temperature limits so as to include in the distillate a somewhat wider boil ing range or a slightly narrower boiling range. for example, 208 F. to 239 F. It is usually desirable to produce a distillate containing at least and preferably 8% or more of toluene. Thus, it was found that` when using an East Texas straight-run gasoline, a concentrate containing from 8% to over 10% of toluene, and in the case'of a West Texas straight-run gasoline aconcentrate containing from 10% to over 15% of toluene, could be produced.

l'I'he narrow fraction taken overhead at I0, and hereafter designated as the toluene concentrate, is fed into the solvent treater I2. A suitable solvent for separating the toluene yfrom the other. constituents of the concentrate is` fed at I3; separated toluene, either with or without solvent, is withdrawn at I6, and the substan tially toluene-free remainder of the toluene concentrate is taken oil at Ill.A

The solvent treater may be of any type suitable for the separation of toluene, such as a liquidliquld solvent extraction apparatus, wherein a liquid solution of toluene in a solvent having selective solvent power for aromatic hydrocarbons is separated from a liquid hydrocarbon phase freed from all or most of the toluene; or an azeotropical distillation column, .wherein toluene is obtained as the distillation residue, either pure or together with some solvent (depending upon the amount of solv'ent added) and other hydrocarbons, together with solvent are separated as a distillate having a'low boiling point. It is preferred, however, to employ a vapor phase extrac- 'retains the toluene in the bottom product while permitting the other constituents of the concentrate to pass off as overhead vapors. Solvents other than phenol which aresuitable for use in the solvent treater I2, and particularly in the extractive distillation step, include cresylio acids, alkyl phenol mixtures, aniline, alkyl anilines, diphenyl amine, ditolyl amines, carbitols l(diethylene glycol mono ethers) such as methyl ethyl, and propyl carbitols, chlorinated dialkyl ethers such as beta-beta-dichlorethyl ether, nitrobenzene, .nitrotoluene, nitroxylenes, naphthols, alkyl naphthols, benzo phenone, phenyl tolyl ketone, v

diphenyl ketone, alkyl phthalates such as dimethyl phthalate, alkyl salicylates such asmethyl salicylate, benzyl alcohol, benz chlorides, i. e. benzyll benzal, and benzo chlorides, benzonitrilfe, diphenyl oxide, ditolyl'oxide, hydroxy pyridine, nitropyridine, chlorinated pyridines, quinoline, isoquinoline, chlorinated quinoline, hydroxy quinolines, 5nitro quinoline, tetra hydro furfuryl alcohol, furfural alcohol, furfural, the mono glycerol ethers such as l-methoxy glycerol, 2-methoxy glycerol, l-ethoxy glycerol, 2-ethoxy glycerol, 1- propoxy glycerol, 2-propoxy glycerol, l-isopropoxy glycerol and 2-isopropxy glycerol, the glycerol, di-ethers such as 1,2-di-methoxy glycerol,

1,3-di-methoxy glycerol, 1,2-di-ethoxy glycerol, 1,3-di-ethoxy glycerol, 1,2-di-propoxy glycerol, 1,3-di-propoxy glycerolh1,2-di-isopropxy glycerol, and r1,3-di-isopropoxy glycerol,the mixed di-glyc- -erol ether esters such as 1-ethoxy,2methoxy glycerol, l-methoxy, 3-propoxy glyerol and 1- ethoxy, z-isopropoxy glycerol.

The toluene obtained through line I5 is freed'of- `the solvent, preferably by fractional distillation,

`l Fl to 1450 F., and preferably 1300 F. to

1400" F., in order to crack it, whereby unsatu .rated hydrocarbons suc-h as oleflnes, dienes, and

aromatics are formed. The timeiof cracking at these high temperatures is governed so as to gasify aboutv 30% to 70%, and preferably 45% to 55%, of the feed per pass, gasification being defined as conversion of the liquid feed to molecules having 5 or lesscarbon atoms.

The heating of the hydrocarbons to the cracking temperature may be achieved by contact with 'a heated solid surface, for example, in an ex- `formed in ternally heated coll as has been described, `or may be realized by admixture of hot substantially inert gases such as ue gases, carbon dioxide, hydrocarbon gases, steam, etc., or by` a combination of both methods. f

`In order to prevent excessive coke formation it is desirable to avoid the contact of ferrous metals with the hydrocarbon at cracking temperatures.

Copper-containing alloys such vas alumium` `or phosphor-bronze, or refractory ceramic materials do not cause rapid coking when used inthe construction of `surfaces exposed to hydrocarbons at y cracking temperature.

Cracking accordingto this invention is preferably purely thermal, i. e, non-catalytic, and is conducted in the absence of catalyst, be itadded catalysts such as gaseous halogenated compounds, solid catalytic metals or oxides, or catalysts presitu, e. g. lustrous carbon orpyrophoric metalsf"` The cracking should be conducted at pressures about atmospheric or below and preferably not substantially above 100 to 150 lbs. p, s. i. Pref-` erably, pressures not in excess of those required to overcome the resistance of the cracking unit are employed. The use of an inert diluent" such as steam is advantageous.

The actual time forwhich the vapors are sub jected to cracking conditions should bebelow about 0.1 second to avoid decomposition of the butadiene formed. This time is, however, very difficult to estimate correctly because of volume variations during cracking. The liquid space velocity is, -on the contrary, easy to estimate and,

for giventemperatureapressures and admixtures, 1

determines the actual vapor space velocity and cracking time. Liquid'space velocity is the volurne of liquid delivered per hour` to the cracking zone, per volume unitvof said zone. The cracking )zone is defined as the space occupied by gases in which the temperature is within 40 F. of the peak temperature. The cracked vapors are rapidly cooled or quenched after passing through the cracking zone. i i

The liquid space velocity which is `chosen depends on the temperature and pressure in the cracking coil. At 1380 F. and atmospheric pressurea liquid space velocity of about 35 resultsin gasification of about 50% and the formation per` The cracked products emergingfrorn `coil `Il are led through line 2l `into column 22 wherein they are fractionallydistilled to separate a C s and i lighter fraction.` 'Ihis fraction, which comprises olefines and `up to 25%to 30% dienes, `passes through overhead line 23 and anaphtha substantially free of lighter hydrocarbons is withdrawn through line 24. This naphtha containsnormally about 16% of toluene and `may `be recycled through lines 24, 6 and 3 to column I to be further treated aspart ofthe above-described feed.

The diene-rich gases in line 23 are advanta` geously treated in zone 20 so as to separate the valuable dienes. This separation may be ,effected by fractional distillation, or bysextractive or azeotropical distillation, or by solvent extraction by means of a polar solvent having greater solvent power fordienes than for mono-olenes and saturated hydrocarbons,` or by selective poiymerization, or by complex formation, tionof these methods, etc.

If the feed introduced through line 3 from the or by a `combinaoutside is relatively poor in toluene, it may'be advantageous,` instead of commingling it with the cracked recyclingnaphtha, toprepare from the latter a separate toluene lconcentrate having a toluene content different from lthat ofthe concentrate in line l0 and introduce the former into the extractor I2 at the same ordiierent level from that at which the latter enters.

Forthis purpose `the column 22 may` be operated so as to yield a bottom fraction substantially free of components boiling below 195 F. and preferably 206 F. by taking in addition` to the gas fraction in line 23 an appropriate side stream through line 30. If desired, two columns`may be used to produce the three fractions". `The bottom fractionis led through lines 24 and 25 to @fractional distillation column 26`, wherein itis -refractionated to yield a light fraction 'boiling below 245 F. and preferably 2319 F., which is removed overhead through line `2li. tion boiling substantially between 195 F. and

245 F. is a cracked toluene concentratewhich comprises most of the `toluene produced inthe cracking. This concentrate is led through line aromatics and paraillns.` Such methods are', for

lil

28 vto `column I 2. `A heavy liquid boiling above 231 F. is withdrawn from column 26 through line` This cracked toluene concentrate `may contain Asubstantial amounts of olenes, and particularly polyoleilnes, produced in the cracking.` Oleiines have `solubilities in Apolar solvents, such as those usel for extractive distillationin column l2, which are intermediate between those of paraflinic hydrocarbons `and of toluene. Thisr'nakes it more dimcult to separate oleiines, and especially polyolenes, than to separate parafiins from toluene by extractive distillation. Thus, it is often advantageous to free the concentrate in line 28 from olenes. This can be done in olene separation zone 29 by one of the methods which eliminates or transforms preferentially polyolenes or polyand mono-olednes without substantially affecting example, absorption in dilute acids such as sul- `i'uric` acids or complex-forming reagents, e. g.

CuCl, AgCl, SO2, etc. Yhydrogenation in the presence of a suitable catalyst such as nickel; copper, etc: or polymerization followed by fractionation, especially catalytic polymerization, in the presence of suitable catalysts such as solid phosphoric acid or one of those listed in National Petroleum News of November 20, `1035, page 45 and following, or in U. S. Patent 2,171,207; `partial oxidation in the presence of a catalyst such as silver, etc., followed byV fractional distillation. etc.; or a combination thereof. y

Referring now to Figure II, which-illustrates an application of this process in .which one concentrate,` e. g. the benzeneor the toluene or the xylene concentrate,` or any two concentrates, or the three concentrates simultaneously,` are being treated.- It will not b. described in regard to the last-mentioned case,it being understood that by proper variation of the flow scheme any other case may be realized.

A hydrocarbon distillate containingaromatics This `fracis admitted from storage not shown through line 3| to fractional distillation zone 32. A suitable distillate produced in the process may be admitted thereto through line 33. In this fractionation 'zone 32 the admitted distillates are fractionated to produce the desired narrow boiling concentrates and separate them from the remainder of the distillate. The concentrates may be conducted through lines 34, 35 and 36 to aromatic separation zone 31. The remainder may be ywithdrawn through lines 38, 39, 40 and 4I. If an aromatic is present in too small quantities in the concentrate to make its recovery worthwhile (e.` g., less than 4%) it may by-pass the aromatic separation zone 31. In this case it is often preferable to conduct the fractional distillation in zone 32 so as to produce a narrower boiling fraction containing only the more desirable nonaromatics. Thus, for example, if benzene is present in but very small amounts a fraction boiling from 170 F. to 185 F. is advantageously obtained 'from zone 32 through line 34 and conducted through line 42 to line 44 which leads to cracking zone50.

The other aromatic-free concentrates may be obtained through'lines 48 and 49 which lead, as well as line 44, to` cracking zone 50. Prior to cracking, these aromatic-free concentrates may be again separated by fractional distillation, each into two fractions, both of substantial proportions, and only the higher boiling cracked. Thus, the benzene-free benzene concentrate may be advantageously separated in fractional distillation column 45 into a bottom portion boiling above 170 F., which isobtained through line 46 and conducted to line 44, and overhead fraction withdrawn through line 41. Other concentrates may be treated similarly, e. g., the toluene-free toluene concentrate may be fractionated in a distilling column not shown to separate constituents boiling below 210 F., which are withdrawn vwhile the remainder is conducted to cracking zone 50. Here the three concentrates are lcracked under conditions similar to those previously described for the toluene concentrate in cracking coils I, 52 and 53. It is preferred to crack the concentrates under independently controlled conditions of time and temperature, as their thermal stability is different, the lower boiling ones being less stable and requiring greater liquid space velocities for the same gasication. If desired, the several concentrates may be combined by means of line 6| and cracked together in one coil.

The .cracked'products after rapid quenching are treated in separation zone 54 to separate therefrom dienes which may be withdrawn through'line 55, ran aromatic-rich naphtha having a broad boiling range taken through line 33 to zone 32, or one or more cracked concen- -trates taken through lines 56, 51 and 58 to zone 31; and other hydrocarbons may be withdrawn at 59 or 60.

Olenes which may interfere with the separation of aromatics or cracking may be separated in separation zone 29 as described above.

The following example may further illustrate this invention:

Example A West Texas straight-run gasoline boiling from about 86 F. to 305 F. was cracked at 1382 F. at a liquid space velocity of 32. The gaseous portion of the cracked products (i. e., gases having less than 6 carbon atoms in the molecule) contained v8.25% of dienes.

A toluene concentrate boiling from 206.6 F. to 230 F.,` and from which the toluene was removed by extractive distillation, gave upon cracking under the same conditions a yield of diene equal to 14.0% of the vapor phase. n

A xylene concentrate prepared from this gasoline and from which the xylenes were removed by extractive distillation, boiled from 257 F. to

268 F. and gave upon cracking under the same Y conditions 12.8% of dienes in the gaseous ucts.

We claim as our invention: l

1. In the process of manufacturing unsaturated hydrocarbons having conjugated double bonds from a petroleum oil boiling over a relatively wide range, the steps comprising separating from said petroleum oil at least two of three narrower fractions, one boiling substantially between 156 F. and 185 F., a second between 195 F. and 245 F. and a third between 260 F. and 300. F.; treating one of said fractions to separate the aromatic hydrocarbons contained therein, combining the remainder of said fraction with one other of said three narrower fractions, subjecting the combined productsto cracking in the vapor phase between 1100 F. and 1450 F. for a time to gasivfy 30% to 70% thereof whereby substantial amounts of unsaturated hydrocarbons having conjugated double bonds are produced and separating said unsaturated hydrocarbons from the resulting cracked products.

2. In the process of manufacturing unsaturated hydrocarbons having conjugated double bonds from a petroleum oil boiling over a relatively wide range the steps comprising separatingfrom said oil a fraction boiling substantially between F. and 185 F. and one of two other prodfractions, the first boiling vbetween 195 F. andv- 245 F. and a second boiling between 260 F. and 300 F., treating oneV of said last-named fractions to separate the aromatic hydrocarbons contained therein, combining the remainder thus obtained with said fraction boiling between 170 F. and F., subjecting the combined products to cracking in the vapor `phase between 1100 F. and l450 F. for 'a time to gasify 30% to 70% thereof whereby substantial amounts of unsaturated hydrocarbons having conjugated double bonds are produced and separating said unsaturated hydrocarbons from the resulting cracked products.

3. In the process of manufacturing unsaturated compounds having conjugated double bonds froml a petroleum oil boiling over a relatively wide range below and above the boiling temperature of toluene, the steps comprising separating two fractions, one boiling between F. and 245 F. and containing most of the toluene comprised in said oil, and the other boiling between 170 F. and 185 F., separating the toluene contained in the former fraction, subjecting the remainder of said former fraction `and the latter fraction to cracking conditions in the vapor phase between 1100 F. and l450 F. for a time to gasify 30% to 70% thereof, whereby substantial amounts of valuable unsaturated hydrocarbons having conjugated double bonds are produced, and separating said valuable hydrocarbons from the re-v sulting cracked products. i MOTT SOUDERS, JR.` RUSSELL N. SHIRAS.

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